Day May 28, 2007

I just got home from Fire in the Sky 2007 in Mansfield, WA. FITS is Washington Aerospace’s spring high-power rocket launch, drawing folks from all over the western U.S. for three days of launches and extreme engineering geekiness.

My friend Bill Barnes and I both tried for, and achieved, our NAR Level 1 certifications, allowing us to build and fly rockets requiring motors with more than 62.5 grams of propellant, and giving between 160 and 640 Newton-seconds of total impulse. I flew the PML Phobos, with a 29mm motor adapter in the 38mm motor mount, to accomodate the H128W motors we used for certification. Both of our flights went picture-perfect with motor ejection; I used a 36" chute with central spill-hole to bring the rocket down gently but fast and straight. I don’t have a good picture of the Phobos launch, unfortunately — the H128W took it off the pad faster than I could hit the shutter release. But Bill and Susan might have video of both our cert flights, so that might be forthcoming when we can get it transferred.

After trudging through the sagebrush and getting woozy from too little water, too much sun, and no
food, I recovered the Phobos (with spotting help from Bill – thanks!) and we completed our cert.

At this point, since I was covered by Kent Newman’s LEUP (thanks!), I was able to fly the Giant Leap Elipse. In order to get the CG properly positioned about 4 inches ahead of the CP (center of pressure), I had to load fishing weights (and a couple of extra AA batteries) into the nose cone. With the 48" TAC-1 parachute, MC2 flight computer, and a 38mm I357 motor, the Elipse weighed in at 7.5 pounds or so — a heavy rocket but the I357 had plenty of punch to get it off the pad The Aerotech I357 generates a total of 342 Newton-seconds of impulse, with a peak thrust of 432.8 Newtons. As a comparison, if you’ve used the black-powder Estes model rocket motors, the D12 delivers a total of 16.8 Newton-seconds of impulse, and 29.7N maximum thrust — so the I357 is delivers about 20x more thrust than a D12.

The Elipse launched perfectly and the TAC-1 chute was easily visible in red and black against the clouds. I managed a picture of the launch itself (shown here, click for a bigger version), which generated a fairly impressive smoke trail and nozzle flame. To get a sense of scale for this picture, the Elipse is 6.5 feet tall and 3 inches in diameter. Recovery was easy since it drifted back towards the pads. I’m thrilled at how the weekend went, and eager to build something new for August or October.